[JoshK]

This is the always asked question when venturing into the low watt class of amplifiers.   So my contribution to this circle is to attempt to summarize some key features for making your speaker/room/amp handjive.

• First realize that now all low watt amps are created equal.  As important to the number of watts in reserve is the output impedance of your amp in determining what speakers should match well or not.  Case in point: My Tannoy Arundel 15" dual concentrics are north of 97db efficient but really aren't as flea watt friendly as that would imply. There is inevitably something about their impedance curve that makes them demand a lower output impedance of the amp driving them which most SET amps are not.  So an experienced flea watt guru will want to examine the true efficiency of the speakers, as well as the impedance curve and phase angle curve of the speakers in question to determine whether they are SET amp friendly.
• If you have a pair of speakers in mind and your choosing the amp, the size of room size, your listening volume habits and how demanding is your taste in music all factor into the equation of how few watts can you get away with.  The bigger the room and/or how far away you sit play a big part as loudness decreases with the inverse square, i.e. you need four times the power for equal loudness at 2m as you do at 1m.  If you listen to little girl with a guitar music you will need less power than full scale orchestral, large choral, dense progressive metal, etc. If you like to headbang while listen to music or play at rock concert levels you obviously need more power.

One can get away with surprisingly little watts if the right set of conditions are met.   I long owned a pair of 91db/w 4ohm MTM speakers which are not the easiest load.  I like spectrally dense music in general and I like to play moderately loud, say upper 80dbs on average (not headbanger, but above polite conversation levels). I had a medium sized room for which I sat a normal 2m back.   I had a 10w SEP (single-ended pentode) amp that would hardly ever flinch at this task.   This leads me to my next point:

The recovery time of your amp upon clipping as well as how nice/ugly it clips have a big factor in choosing an amp that does not have a huge power reserve on tap.  If the recovery time of the amp is near instantaneous and the clipping is soft (i.e. compression rather than true wave-form clipping) then it is hardly even noticed.  This drives a lot of what I like about some of the better lower powered amps.

There are lot of folks that believe in huge overkill when it comes to power reserve.  I am not one of them.  If these amps were as good at the one watt level as some of the simple low powered amps then it would be a no-brainer, but for most of us here, we believe that is simply not so. 

Many of this brute amps employ lots of feedback.  Take a look at a typical THD vs power curves for these amps and you'll notice something funny in the (typically) less than 10w range.  THD rises!  Why is that?  Because of the feedback.   Unfortunately this comprises 99% of your listening.  So do I want to trade off the 99% for the 1% crescendo?  Not me.

[rollo]

  Very good info here thanks for sharing and taking the time to do so.


charles

[JoshK]

Its intended as a start.  We can flush out the details with time.  I just foresaw the numerous questions in this regard and pre-empted.

[Diamond Dog]

There are lot of folks that believe in huge overkill when it comes to power reserve.  I am not one of them.  If these amps were as good at the one watt level as some of the simple low powered amps then it would be a no-brainer, but for most of us here, we believe that is simply not so. 

Many of this brute amps employ lots of feedback.  Take a look at a typical THD vs power curves for these amps and you'll notice something funny in the (typically) less than 10w range.  THD rises!  Why is that?  Because of the feedback.   Unfortunately this comprises 99% of your listening.  So do I want to trade off the 99% for the 1% crescendo?  Not me.

 

D.D.

[JoshK]

I do not wish this to denigrate into the typical SS vs Tube war, but what exactly is confusing DD?  Your picture says what I am saying.

What is not pictured in that graph, is although the level of THD is low, the spectral distribution of the THD is undoubtedly comprised of upper harmonics for which our hearing acuity is far greater.

Additionally, crossover distortion which is very hard to measure in those standard methods, has been demonstrated to be audible. 

I am making some broad generalizations which are to be used merely as guides for the novice, not set in stone guidelines for what has to be.

[medium jim]

I would love to have my Altec A7's that were something like 102db as I could run SET. 

Jim

[Freo-1]

I do not wish this to denigrate into the typical SS vs Tube war, but what exactly is confusing DD?  Your picture says what I am saying.

What is not pictured in that graph, is although the level of THD is low, the spectral distribution of the THD is undoubtedly comprised of upper harmonics for which our hearing acuity is far greater.

Additionally, crossover distortion which is very hard to measure in those standard methods, has been demonstrated to be audible. 

I am making some broad generalizations which are to be used merely as guides for the novice, not set in stone guidelines for what has to be.

Good post!  Thanks, Josh.

I tried to get a discussion about this awhile back with a question:   "Is all wattage created equal?".

The intent of that question was to get into subjects like low wattage amps, class A vs. class AB,  single ended vs. push/pull, etc. and what sonic differences can be picked up.

Some of the distortions heard when listening are not easily measured, but as you state, can be audible.

[R_burke]

I use Manley Mahi monoblocks and they have both Triode and Ultralinear mode which changes the output.  Additionally they have "adjustable" feedback which also changes the output.  The specs also take into consideration the load they are driving

Here are the advertised specifications:

into 5 ohms:   TRIODE   UL
        FB MIN:   18W   20W
        FB STD:   27W   42W
       FB MAX:   28W   46W
into 8 ohms:   TRIODE   UL
       FB MIN:   14W   24W
       FB STD:   24W   40W
       FB MAX:   25W   41W

[TONEPUB]

Single driver speakers work great, the greater the sensitivity the better and I've found the simpler the crossover the better, though
there have always been a few exceptions to the rule...

[JoshK]

Good post!  Thanks, Josh.

I tried to get a discussion about this awhile back with a question:   "Is all wattage created equal?".

The intent of that question was to get into subjects like low wattage amps, class A vs. class AB,  single ended vs. push/pull, etc. and what sonic differences can be picked up.

Some of the distortions heard when listening are not easily measured, but as you state, can be audible.

Its a loaded topic.  I was being quite general.  Plenty of exceptions, but the guidelines certainly lead you down the right thought process hopefully. 

Single drivers don't have as many issues with phase angle through the crossover region, which makes them easier in general, but there are exceptions in both camps.  I think part of the issue is the speakers need to be designed with those goals in mind.

[bunky]

I run a 93.5 db pair of Silverline Sonata Mk III with a 18 watt SET amp and it can play louder than i need it to in my 14' x 25' listening room.

[Freo-1]

• If you have a pair of speakers in mind and your choosing the amp, the size of room size, your listening volume habits and how demanding is your taste in music all factor into the equation of how few watts can you get away with.  The bigger the room and/or how far away you sit play a big part as loudness decreases with the inverse square, i.e. you need four times the power for equal loudness at 2m as you do at 1m.  If you listen to little girl with a guitar music you will need less power than full scale orchestral, large choral, dense progressive metal, etc. If you like to headbang while listen to music or play at rock concert levels you obviously need more power.

One can get away with surprisingly little watts if the right set of conditions are met.   I long owned a pair of 91db/w 4ohm MTM speakers which are not the easiest load.  I like spectrally dense music in general and I like to play moderately loud, say upper 80dbs on average (not headbanger, but above polite conversation levels). I had a medium sized room for which I sat a normal 2m back.   I had a 10w SEP (single-ended pentode) amp that would hardly ever flinch at this task.   This leads me to my next point:

The recovery time of your amp upon clipping as well as how nice/ugly it clips have a big factor in choosing an amp that does not have a huge power reserve on tap.  If the recovery time of the amp is near instantaneous and the clipping is soft (i.e. compression rather than true wave-form clipping) then it is hardly even noticed.  This drives a lot of what I like about some of the better lower powered amps.

There are lot of folks that believe in huge overkill when it comes to power reserve.  I am not one of them.  If these amps were as good at the one watt level as some of the simple low powered amps then it would be a no-brainer, but for most of us here, we believe that is simply not so. 

Many of this brute amps employ lots of feedback.  Take a look at a typical THD vs power curves for these amps and you'll notice something funny in the (typically) less than 10w range.  THD rises!  Why is that?  Because of the feedback.   Unfortunately this comprises 99% of your listening.  So do I want to trade off the 99% for the 1% crescendo?  Not me.

Excellent observations. 

My current low wattage amp is a Pass Labs M2, a 25 watt zero feedback class A push pull unit that sounds a lot like a lower powered tube amp.  There is something about class A and zero feedback that just sounds so right. 

Will look into some DIY SET designs with my tech buddy, who has a large cache of iron and tubes to choose from. 

These speakers are from Cary, and work pretty well with as little as 10 watts: 






Of course, want to learn more about speakers with these low wattage beauties.

[medium jim]

A good friend of mine has a pair of Avantgarde Trio's that he tells me are 107db.  However, he currently is driving them with a pair of Marantz 9's in triode (40watts).  Funny thing, I have the same amps and drive my less than efficient Magnepan's...

Another wonderful speaker for low wattage is Klipsch corner horns or LaScala's.

Jim

[Freo-1]

A good friend of mine has a pair of Avantgarde Trio's that he tells me are 107db.  However, he currently is driving them with a pair of Marantz 9's in triode (40watts).  Funny thing, I have the same amps and drive my less than efficient Magnepan's...

Another wonderful speaker for low wattage is Klipsch corner horns or LaScala's.

Jim

I have listened to K-Horns with custom crossovers connected to McIntosh 225's.  Very lifelike sound with some types of music.

[JoshK]

The only Klipsch I heard were cornwalls, iirc.  They were good in some ways but a bit harsh when driven hard.  I think modern horns/CDs can do better, but Mr. Klipsch was infamously cheap. 

[Diamond Dog]

JoshK : re SS vs. tube - I actually have both in my current system and am currently seriously considering a pair of SE/PP monos so I don't really have a dog in that fight...If you guys are gonna go to DEFCON 2 whenever someone from outside this segment of "The Hobby" has a question or is looking for a clarification on something, it doesn't bode well.

Freo-1 : Maybe you can let us all know at the outset whether this is the kind of Circle which is going to promote the concept of welcoming new people exploring the idea of low-wattage systems or if it's the kind of Circle which basically serves as a treehouse where a few existing enthusiasts get together to slap each other on the back...

D.D.

[JoshK]

JoshK : re SS vs. tube - I actually have both in my current system and am currently seriously considering a pair of SE/PP monos so I don't really have a dog in that fight...If you guys are gonna go to DEFCON 2 whenever someone from outside this segment of "The Hobby" has a question or is looking for a clarification on something, it doesn't bode well.

D.D.

That is fine.  I am open for real discussion, but when your post consisted merely of a chart (which showed precisely what I was talking about), and an emoticon, it looked a though you were merely trolling.   If you had a serious question, you could have simply articulated such rather than a passive aggressive bait.

Let me rephrase that.  Did you actually have a question, or were you merely taking a stab? 

There is no back slapping "in-crowd" that you suspect.  I was in the "other" camp for most of my audiophiledom, but I learned that that wasn't what I find realistic in sound quality.  Then again neither are a lot of hi-eff/low watt systems.  Its a delicate balance.  I also like other designs, but there is something special about a SET amp and the right system when it gels.

[smk]

I think as well SPL/W/m & listening volume habits, one of the most important but overlooked thing low-wattage amps speakers which you hit on is the speaker load throughout the bandwidth.

I have a pair of 94/dB/m speakers SDLs & they work just fine in my small listening room with 2 watts/channel as long as exercise discretion with the volume control.

[JohnR]

JoshK - thanks for getting right to a number of key issues. 

[Ericus Rex]

That is fine.  I am open for real discussion, but when your post consisted merely of a chart (which showed precisely what I was talking about), and an emoticon, it looked a though you were merely trolling.   If you had a serious question, you could have simply articulated such rather than a passive aggressive bait.

+1